A touch panel is known as a coordinate input device used for a computer, an information processing device, or the like.
As a general touch panel, a projection capacitance two-dimensional touch panel is known. The projection capacitance two-dimensional touch panel has various problems as below.
According to the projection capacitance two-dimensional touch panel, an air-gap, a protective plate, and the like are normally provided on a sensor section. This causes a signal to be received by the sensor section to be smaller. Therefore, an SN of a detection signal cannot be sufficiently obtained and, accordingly, the detection signal is undistinguishable from an electric field noise or a thermal noise radiated from another device. It follows that a practical detection accuracy cannot be obtained. As a result, the following problems occur. That is, a hover operation serving as an extended function of the touch panel, and a finger direction detecting function cannot be carried out. Further, an input function with use of a pen having a tip with a small area cannot be carried out.
Drive electrodes (whose number is M) and receiving electrodes (whose number is N) have M×N intersections. According to a pulse scan method, the intersections are detected one by one in time series. In view of the circumstances, it is necessary to detect each of the intersections in a short time. Therefore, in a case where a panel is larger in size and more intersections are accordingly detected, a problem further occurs such that the SN of the detection signal cannot be sufficiently obtained.
Note that, in a case where the intersections are detected independently of driving of a display so as to secure a sufficient detection time, the projection capacitance two-dimensional touch panel is subjected to electrostatic radiation while display electrodes of the display are being driven. Unfortunately, this causes a noise in touch panel detection.
In view of the circumstances, for example, Patent Literatures 1 and 2 each disclose a proposal of a method for increasing, by M-sequence driving, the number of intersections to be detected during one clock scan so as to secure a sufficient detection time.
The M-sequence driving enables an increase in number of the intersections to be detected during one clock-scan. This allows a longer detection time for each of the intersections. As a result, it is possible to increase the SN of the detection signal.
This makes it possible to solve the various problems caused by the problem such that the SN of the detection signal cannot be sufficiently obtained.